Antibiotics are commonly prescribed to fight bacterial infections, but after taking the medication, you may experience diarrhea, an antibiotics side effect. Antibiotics work by killing or reducing the growth of certain bacteria that are making you ill, but they can also kill good, or helpful, bacteria in your intestinal system. This may disrupt the delicate balance in your intestines, allowing bad intestinal bacteria that are resistant to the antibiotic to increase.

“You’re upsetting the normal fecal flora [microorganisms], and that can lead to diarrhea,” says Henry Parkman, MD, a gastroenterologist and the vice chair of research in the department of medicine at Temple University's Lewis Katz School of Medicine in Philadelphia.

Antibiotics and Diarrhea: Understand the Reaction

Any antibiotic can cause you to have diarrhea, whether you take it orally or by injection, but broad-spectrum antibiotics — antibiotics that kill a wide range of bacteria — are the most likely to affect you. These include Cleocin (clindamycin), certain types of penicillin, and cephalosporins.

Most of the time, diarrhea as an antibiotics side effect is mild and will stop on its own or when you stop taking your medicine. However, “antibiotic-associated diarrhea is also seen a lot in patients who are hospitalized or in nursing homes,” says Dr. Parkman. And then it can be more serious. In some elderly, ill, and hospitalized patients, antibiotics can result in a Clostridium difficile (C. diff) infection, which can produce a toxin that can lead to serious complications such as inflammation in the colon wall (colitis), severe dehydration, or toxic megacolon, in which the colon becomes distended and may rupture.

Protect Yourself

Some patients find they can take certain antibiotics and diarrhea won’t be a problem, but taking other drugs will cause diarrhea, Parkman says. If you have diarrhea from taking antibiotics, especially if symptoms persist or worsen, call your doctor. If it’s necessary for you to continue antibiotics treatment, your doctor may be able to switch you to another drug that won’t have this side effect.

If you’re taking an antibiotic, consider changing your diet for a few days to avoid foods that commonly trigger diarrhea, such as dairy products, fatty foods, spicy foods, and foods high in fiber like whole-grain breads, cereals, and beans. You should also sip water and skip caffeine and alcohol. If your symptoms of antibiotic-associated diarrhea are severe, your doctor may recommend bed rest, intravenous fluids to replace your electrolytes — sodium, potassium, and chloride — and another antibiotic to treat the bad intestinal bacteria that is causing diarrhea.

Probiotics May Relieve Diarrhea

Probiotics are friendly bacteria or yeast that help your digestive system function properly. A growing body of research shows that probiotics may help protect against antibiotic-associated diarrhea. In particular, some people have found that the probiotic Lactobacillus acidophilus, found in certain brands of yogurt, helps reduce antibiotic-associated diarrhea in adults. Probiotics are also found in miso and other fermented foods.

Probiotics occur naturally in some foods, are added to others, or can be taken as concentrated supplements. “There are hundreds of probiotics,” Parkman says. “Each one is a little different. You may need to experiment to determine which one, if any, works for you.”

Probiotics supplements are sold in drugstores, groceries, and health food stores in liquid, powder, and capsule forms. They are sometimes kept in a refrigerated section because they need to be protected from heat. You should talk to your doctor before taking probiotics, to make sure they’re safe to use with your other treatment plans.

A Prescription for Caution

To avoid antibiotic-associated diarrhea, it’s best to take antibiotics only when your healthcare provider believes they are absolutely necessary. Antibiotics do not combat viral infections such as the cold and flu; they are effective only against bacterial infections.

Adjusting your diet may help you avoid or ease diarrhea symptoms until you finish your antibiotics regimen. Drink water to stay hydrated and replace any fluids lost to diarrhea. Most important, if your symptoms worsen or don’t clear up after you take your medication, talk to your doctor.